A tornado is a violent rotating column of air which is usually funnel-shaped and is associated with thunder storm and cloud activity. While tornados have been recorded throughout the United States, the areas most affected are Texas, Oklahoma, Kansas and Missouri. Tornados also occur in other parts of the world as in West Africa and India. Each year tornados cause thousand of dollars of damage.
A great deal of research has been carried out with respect to the causes of tornados and the prediction of tornado activity so as to provide early warning. One significant development is the use of doppler radar in the study of tornados. Through the use of doppler radar and visual observation, much has been learned of the structure and motion of tornados and numerous articles on this subject have been published. Among these are the following:
Airflow and Precipitation Trajectories Within Severe Local Storms Which Travel to the Right of the Winds; By: Keith A. Browning; PA0 Journal of The Atmospheric Sciences November 1964 Volume 21 Pages 634 to 639; PA0 Wake Vortex Structure and Aerodynamic Origin in Severe Thunderstorms By Leslie R. Lemon; PA0 Journal of The Atmospheric Sciences April 1976 Volume 33, No. 4, Pages 678 to 685.
It has been observed that severe local storms in the northern hemisphere travel to the right of the winds in the middle troposphere. Such storms are referred to by Browning as SR storms (S for "severe" and R for "right"). The storms travel in a general direction from west to east. Rain--frequently very heavy--generally occurs to the north and east of the center of the storm while hail frequently occurs to the northwest and west. In a south southwest quadrant the air is usually clear.
In the northern hemisphere tornados generally rotate in a counterclockwise (anticyclonic) direction. Up drafts and down drafts coexist continuously in the storm, each gaining kinetic energy not only from a conversion of potential energy but also directly from the kinetic energy of the relative horizontal inflow. The tendency of severe local storms to travel to the right of the winds increases the flux of air entering both the up and down drafts. Horizontal flow continues to converge anticyclonically toward the eddy center. The relative motion of the winds in the lower and middle troposphere toward the storm's right flank is responsible for the characteristic organization and structure of this kind of storm.
Efforts have been made not only to forecast but also to reduce the tremendous devasting effect of such storms, for example by cloud seeding. However, no significant success has been achieved in reducing damage done by tornados.